What Covid has taught us about respiratory viruses

Airborne transmission could play a greater part in spreading infection than was thought

The pandemic is challenging traditional assumptions about the spread of viruses. Photo: Getty

The coronavirus pandemic has revealed critical gaps in knowledge about how respiratory viruses spread between people, scientists have said.

The findings, which could change the way the next health crisis is handled, were reported in a review published on Thursday.

“During the emergence of novel respiratory viruses, a more holistic approach that acknowledges all modes of transmission – airborne, droplet and fomite – is needed to successfully mitigate risk and prevent spread,” said the report, by the American Association for the Advancement of Science.

“The requirement for direct evidence of infectiousness of sampled aerosols before acknowledging and adding controls to address airborne transmission leaves people at potential risk.”

In the review, author Chia Wang looks at how research on the airborne transmission of respiratory viruses allowed for better-informed controls to reduce and mitigate airborne transmission.

Large respiratory droplets produced by the coughs and sneezes in sick people were traditionally thought to be the main way a virus spread among people.

Now, a growing body of evidence indicates that many of the respiratory pathogens, including the one that causes Covid-19, spread through virus-laden microscopic respiratory aerosols.

Learning from Covid

Until recently, most respiratory pathogens were believed to spread mainly through coughed droplets or through contaminated surfaces.

That understanding has largely guided public health recommendations in mitigating viral spread.

But several respiratory pathogens, including influenza and the common cold, are known to also spread by way of infectious respiratory aerosols, which can float and travel in airflows at far greater distances and for much longer, infecting those that inhale them.

The growing evidence, much of it gained from studying the spread of Covid-19, suggests airborne transmission may be a more dominant mode of respiratory virus transmission than previously thought.

“The World Health Organisation and many national public health agencies recommend maintaining physical distances of either one or two metres. However, this distance is not sufficient to protect against aerosols that travel beyond this range,” the report said.

“If large droplets dominated transmission, distancing alone would have effectively suppressed the transmission.

“As has been repeatedly shown in superspreading events, airborne transmission occurs in poorly ventilated rooms when occupants inhale infectious room air.

“Additionally, although distancing helps by moving people away from the most concentrated parts of respiratory plumes, distancing alone does not stop transmission.”